The invention relates generally to electrical control of power consumption on lighting loads, and other voltage-regulatable loads found such as in office buildings, industrial plants, schools and other buildings. The lighting loads to be controlled are both incandescent types and discharge types (such as fluorescent loads).
Prior art devices for regulating lighting loads include transformers connected in either a bucking or boosting circuit configuration. Such transformers normally form a static condition without any dynamic control. The absence of dynamic control either makes it difficult to maximize power saving or alternatively prevents normal operation when the voltage level drops too low or rises too high.
Prior art transformer devices which have controls such as variacs generally have not had adequate sensing circuits to provide for the desired control of power consumption in lighting loads.
Prior art devices for regulating lighting loads have also employed solid state elements. Such solid state elements are generally phased control devices which have a number of undesirable characteristics. For example, they tend to cause a significant amount of radio frequency interference (RFI). They are not generally usable with fluorescent lights without some special provision in the transformer of the fluorescent light. Since they are not generally usable with fluorescent lights, they cannot be used in a circuit which has a mixture of incandescent and fluorescent lights. Furthermore, generally there is no protection against voltage surges in the triac, the diac or other solid state control elements. This absence of protection frequently causes the solid state control elements to be damaged upon the occurrence of a burn out of the lamp.
Another factor to be considered is the existence of a large installed base of lighting circuitry. In order to be effective, it is desirable to have a power control unit which is utilizable in existing lighting facilities as well as in new facilities.
In view of the above background of the invention, there is a need for an improved power control unit for use in controlling lighting loads or other voltage-regulatable loads of all types.